Method of producing a titanium carbide-containing hard metallic composition of high toughness



United States Patent Ofiice 3,490,901 Patented Jan. 20, 1970 METHOD OF PRODUCING A TITANIUM CAR- BIDE-CONTAINING HARD METALLIC COM- POSITION OF HIGH TOUGHNESS Takeji Hachisuka, Toyama-shi, Japan, assignor to Kabushiki Kaisha Fujikoshi, Toyama, Japan No Drawing. Filed Dec. 4, 1967, Ser. Nq. 687,430 Claims priority, application Japan, Oct. 24, 1966, 41/70,093; Dec. 3, 1966, 41/79,115 Int. Cl. B22f 3/16 US. Cl. 75203 4 Claims ABSTRACT OF THE DISCLOSURE A method of producing a titanium carbide-containing, hard metallic composition capable of being formed into articles of high toughness by standard powder metallurgical techniques, the composition comprising, as a major component, titanium carbide and one or more heterogeneous carbides selected from the group consisting of tungsten carbide, tantalum carbide and niobium carbide, and as a minor component, one or more metals selected from the group consisting of molybdenum, tantalum, and tungsten, and one or more iron group metals or iron group metal based alloys, characterized by preliminarily heating a powdery mixture composed of titanium carbide and at least one of the foregoing metals selected from the group consisting of molybdenum, tantalum and tungsten, to cause the formation of a solid solution carbide, and crushing the resulting bonded mass consisting of the solid solution carbide into a fine powder which is ready for use as raw material powder from which said metallic articles are produced.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a method of producing a hard metallic composition which comprises, as maj r ingredients, titanium carbide and one or more carbides, such as, tungsten carbide, tantalum carbide, niobium carbide and the like, and, as minor ingredients, one or more metals, such as, molybdenum, tantalum and tungsten, and one or more metals of the iron group, or one or more iron group metal based alloys. It is a primary object of this invention to provide a metallic composition exhibiting high hardness and toughness.

Description of the prior art Among various cemented carbides which have been widely used, most alloys are composed of, as a main component, tungsten carbide, as an auxiliary component one or more heterogeneous carbides, and a metal of the iron group, such as, cobalt, which serves as a binding agent. Iri'su'ch cemented carbides, the presence or incorporation of the foregoing heterogeneous carbide is not always necessary. The term heterogeneous carbide is designated, for convenience, with the intention of indicating a carbide other than tungsten carbide, such as, titanium carbide, tantalum carbide, niobium carbide, and the like.

In the production of such cemented carbides, containing the heterogeneous carbide, the incorporation of titanium carbide is effected in order to impart the superior heat resistance and high hardness, inherent in the titanium carbide cemented alloy, whereby there is produced a superior alloy (metallic composition) exhibiting high hardness, high oxidation resistance, and high cratering resistance. The material is suitable for use in cutting tools for steel. Since the incorporation of titanium carbide simultaneously brings the unfavorable result of lowering the toughness thereof, the second heterogeneous carbide or carbides, such as tantalum carbide and niobium carbide, are frequently incorporated or added, in combination therewith, at the same time, for the purpose of making up the foregoing deficiency. Among these heterogeneous carbides, titanium carbide is especially added in the form of either a solid solution carbide wi.h tungsten carbide or a solid solution carbide with tungsten carbide and tantalum carbide in general, with the intention of preventing the toughness from being lowered upon the addition, with ut decreasing the effect of the addition of titanium carbide. In spite of the painstaking designs as are taken in the addition of the secondary heterogeneous carbide or in the employment of a solid solution carbide, a lowering in the toughness of the alloy upon the addition of titanium carbide cannot be avoided. In the case of alloys for steel cutting, for example, the amount of titanium carbide to be added is restricted within a certain range mainly from the viewpoint of preserving toughness, and the titanium carbide content of alloys is usually not greater than 20% by weight.

As for titanium carbide base cermets, i.e., metallic compositions which comprise a large proportion of titanium carbide and the balance of one or more heterogeneous carbides selected from the group consisting of tantalum carbide, niobium carbide, molybdenum carbide, vanadium carbide, chromium carbide and the like, inclusive of an iron group metal or iron group metal based alloy serving as a binding agent, the proportion of the heterogeneous carbide being zero in some cases, they are generally used as materials for high temperature use. In this case, a heterogeneous carbide or carbides are added in the form of either a single carbide or a solid solution carbide. The foregoing cermets, suitable for use as a heat resisting material, generally contain 40-50% by Weight of binder metal and have poor wear resistance due to low hardness, therefore they are unfit for tool materials. Even if the hardness thereof is increased by lowering the content of binder metal, they remain as unfit as ever because the brittleness thereof becomes too great.

In the production of a metallic composition or alloy which has an improved or lower brittleness, as well as sufiicient hardness and toughness for use as tool materials, it has been known that the addition of one or more metals, such as, molybdenum, tantalum and tungsten is effective. To this end there is chiefly employed TiC-Ni-Mo alloys. Since the foregoing cermet for use as tool materials, however, contains generally as large an amount of titanium carbide as from 50 to percent by weight, it is inferior to cemented carbides with respect to toughness and has poor thermal shock properties and low thermal conductivity, so that a limitation is placed on the range of its use in some cases, even in the field of steel cutting.

As will be clearly understood from the facts hereinbefore described, a titanium carbide containing metallic composition or alloy has a low degree of toughness due to the titanium carbide which itself is brittle, thereby some limitations are frequently imposed on the content of titanium carbide and the. range of use thereof. Therefore, it is very important to produce a metallic composition or alloy of the class and exhibiting a superior toughness.

Although the reason why the toughness of a metallic composition is improved by the addition of metal such as molybdenum has not yet been completely explained, the effect of molybdenum addition, in the case of a TiC- Ni-Mo alloy, may be explained by the following mechanism: It has been known that molybdenum becomes ready for conversion into Mo C at about 800 C., during sintering, is nearly completely carburized at about 1000 C., and forms a solid solution carbide with titanium carbide at about 1200 C. The surfaces of titanium carbide grains are coated with the solid solution carbide (TIC'MOZC) as thus formed. During the course of the reactions just described, molybdenum reacts first with free carbon contained in titanium carbide powder as a raw material, to form a carbide, so that it may be concluded that the molybdenum serves to increase the purity of the raw material powder. In addition to this, the solid solution carbide (TIC'MOZC) which is produced subsequently forms a rigid bond with a binder metal, because it has a higher wettability for nickel than that of titanium carbide, so that it may be reasonable to conclude that the mutual bonding among hard phases with the advance of grain growth is controlled, with an improvement in the toughness.

SUMMARY OF THE INVENTION With the intention of extending the range of use of a hard metallic composition composed mainly of titanium carbide by improving the toughness thereof and by increasing further its thermal shock resistance and thermal conductivity, a hard metallic composition or alloy of this kind is further incorporated with one or more heterogeneous carbides such as tungsten carbide, tantalum carbide, niobium carbide and the like, in accordance with the method of this invention. More particularly, a blend composed of titanium carbide, one or more metals selected from the group consisting of molybdenum, tantalum and tungsten, and iron group metals or iron group metal based alloys, if desired, the latter being omitted, is first heated in principle to a temperature below an eutectic point at which there is observed the formation of a liquid phase, to convert molybdenum, etc., into carbides and then into solid solution carbides. The resulting bound mass thus produced is subjected to crushing to prepare a raw material powder for the successive process. Secondarily, the foregoing raw material powder composed of solid solution carbides and iron group metals or the metal based alloys, is combined with one or more materials selected from the group consisting of tungsten carbide, tantalum carbide and niobium carbide in the form of a single carbide or a solid solution carbide, if necessary, together with a properly calculated additional amount of iron group metal or the iron group metal based alloy, to prepare a powdery batch from which a hard metallic composition or alloy exhibiting a high toughness is produced by the application of powder metallurgical techniques.

To add one or more heterogeneous carbides such as tungsten carbide, tantalum carbide and niobium carbide to a metallic composition or alloy of this kind, some methods are available; first, these carbides may be added thereto in the form of a single carbide; and second, they may be added thereto in the form of a solid solution carbide with titanium, as in the case where a cemented carbide is prepared. Comparing a metallic composition Example Powdery titanium carbide, metallic nickel and molybdenum are weighed to produce 500 g. of a powder mixture of the composition: 75% TiC20% Ni5% Mo on a weight basis. The mixture is subjected to a wet milling for 50 hrs., together with TiC-Ni-Mo balls and acetone, in a 2 liter ball-milling pot lined with Hastelloy B. After evaporating off acetone to dryness, the milled powder is mixed with a 3% by weight solution of paraffin dissolved in carbon tetrachloride in a concentration of 10% by weight, and is closely stirred to evaporate off the carbon tetrachloride, followed by sieving through a No. 8 mesh. The powder is shaped into a compact under pressure of 0.5 t./sq. cm. while using a cylindrical die of 50 mm. diameter, and the compact is heated to 600 C. in a hydrogen furnace to remove parafiin therefrom. Although paraflin is used to form a compact of possibly high density, while with the intention of accelerating the reaction of molybdenum with titanium carbide, the addition of parafiin is not always necessary. In other words, molybdenum can favorably be activated by suitably controlling the milling condition and/or the grain size in place of effecting such a shaping procedure. Nickel is also added for the purpose of accelerating the reaction of molybdenum, and exhibits a very high effectiveness even in a small amount, as low as a few percent. The addition of nickel has rather a reverse effect in a large amount, in certain cases, so that there is no necessity for strictly adjusting the amount thereof. The compact is heated to 1200 C., for 2 hours, in a vacuum furnace maintained under pressure of 10- mm. Hg, after the removal of paraflin. By means of an X-ray deffraction method carried out in the cold condition, it is confirmed that molybdenum is converted into a carbide Mo C, and then into a solid solution carbide, TIC'MOZC, upon heating. Since a sintered body thus produced is of a very high porosity, it is easily crushed into a fine powder below 80 mesh in size while using a mortar. By the term cermet powder, I mean for the present context, the fine powder thus obtained.

To prepare 1 kg. of a powdery blend of the composition: 30% TiC46% WC10% TaC-12% Ni-2% Mo on weight basis, the foregoing cermet powder, tungsten carbide, tantalum carbide and nickel are weighed and mixed with one another (see TWC in Table I). With the intention of preparing two powdery blends (TWA and TWB) of the same composition as the TWC and to be compared with the TWC, the same procedure as in the preparation of the TWC is repeated with the exception that the titanium carbides to be incorporated are of the single carbide form for the TWA, and of the solid solution carbide form comprising titanium carbide, tungsten carbide and tantalum carbide, for the TWB.

TABLE I Composition of a powdery blend from which a metallic composition (30% Tic-46% WC10% TaCl2% Ni2% M0) is produced on a percent by weight basis Cermet 50 WG-50 'IiO TiC-20 TaC powder TiC WC TaC solid solution solid solution Ni Mo TWA 30 46 10 12 2 TWB 6 30 50 12 2 TWC 40 46 10 4 produced in accordance with the method of this invention with that which was produced while employing any of prior methods of adding heterogeneous carbides, it was confirmed that the former had a toughness far higher and a hardness higher than the latter.

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be more closely described by the following example.

produced is of good porosity, and their characteristics are tabulated in Table II.

TABLE II Characteristics of metallic compositions produced in accordance with the As can clearly be seen from the example above described, a metallic composition produced in accordance with the method of this invention has a toughness far higher and a hardness higher than any of the above compared metallic compositions which are identical therewith in point of chemical composition but are produced according to other methods. In spite of a relatively high titanium carbide content (30% on Weight basis), which is considerably higher than in ordinary cemented carbides of the metallic composition of this invention, it exhibits a transverse rupture strength higher than and a hardness approximately equal with that of the cemented carbide so that it may be concluded that the metallic composition of this invention is superior to any of conventional cemented carbides, when viewed as a titanium carbide containing alloy.

Table III shows results of a series of experiments in which a metallic composition of this invention and a conventional cemented tungsten carbide for steel cutting use are tested to see their cutting efficiencies in the case where the side face of a ring-shaped article is cut. From the results showing the fact that the amount of wear of the former at the cutting edge is very small and the former has a very long durable time of life against fatigue caused by repeated applications of heat and stress at the time of cutting, it may be concluded that the former is superior to the latter.

TABLE III Experimental results from a series of tests carried out to see cutting efliciencies of a metallic composition of this invention and of a cemented tungsten carbide for steel cutting use Kind of alloy: Number of articles cut Metallic composition of this invention (TWC) Super hard alloy of the WC system (P20) Cutting conditions:

Cutting machines-Automatic engine lathe of the exclusive use type. Material to be cut--High carbon chromium bearing steel (SUI 2): 47 mm. 4) x 39 mm. as x 14 mm. Peripheral cutting speed130 m./min. Depth of cnt-0.71.0 mm. Feed0.4 mm./ rev.

From the descriptions hereinbefore stated, it may therefore, be reasonable to conclude that titanium carbide containing metallic compositions produced in accordance with the method of this invention have a wide range of uses, for example, as high temperature materials, bearing materials, as well as steel cutting tool materials, which have previously been satisfied with cemented tungsten carbides.

What is claimed is:

1. A method of producing a titaniumcarbide-containing, hard metallic composition capable of being formed into articles of high toughness by standard powder metallurgical techniques, comprising preliminary heating a powdery mixture composed of titanium carbide and at least one of the metals selected from the group consisting of molybdenum, tantalum and tungsten, whereby a solid solution carbide is formed, crushing the resulting bonded mass consisting of said solid solution carbide into a fine powder, combining said fine powder with a heterogeneous carbide selected from the group consisting of tungsten carbide, tantalum carbide and niobium carbide, said heterogeneous carbide being in the form of a single carbide or a solid solution carbide, wet milling the resulting mixture with an organic solvent, shaping the mixture into a compact, heating said compact to remove said solvent and sintering under a reduced pressure in vacuo.

2. The method of claim 1 further comprising adding to said powdery mixture a metal selected from the group consisting of an iron group metal and iron group metal based alloys.

3. A composition produced by a method according to claim 1, said composition comprising, as a major component, titanium carbid and at least one heterogeneous carbide selected from the group consisting of tungsten carbide, tantalum carbide and niobium carbide, and, as a minor component, at least one metal selected from the group consisting of molybdenum, tantalum, and tungsten, and a member selected from the group consisting of an iron group metal and an iron group metal based alloy.

4. A composition produced by a method according to claim 2, said composition comprising, as a major component, titanium carbide and at least one heterogeneous carbide selected from the group consisting of tungsten carbide, tantalum carbide and niobium carbide, and, as a minor component, at least one metal selected from the group consisting of molybdenum, tantalum, and tungsten, and a member selected from the group consisting of an iron group metal and an iron group metal based alloy.

References Cited UNITED STATES PATENTS 3,165,822 1/1965 Beeghly -203 X FOREIGN PATENTS 500,114 l/ 1939 Great Britain. 573,463 4/ 1959 Canada. 589,321 12/1959 Canada. 617,587 4/1961 Canada. 708,525 5/1954 Great Britain.

CARL D. QUARFORTH, Primary Examiner A. J. STEINER, Assistant Examiner US. Cl. X.R. 29-182]; 75-204, 213 

